1. Field of the Invention
The present invention relates to an image display apparatus and, more particularly, to an image display apparatus suitable for a so-called head mounted display (to be abbreviated as an HMD hereinafter) which is mounted on a head portion, guides a light beam including image information from an image generation means to the eyes of an observer via an optical system, and displays an image displayed on the image generation means as a virtual image.
2. Related Background Art
In one conventional HMD system, an image is displayed for the observer by directly enlarging the image on an image generation means such as a liquid crystal element (LCD), a CRT, or the like using a coaxial lens system.
Another HMD employs a decentered optical system as an optical system to increase the display field angle and to obtain a good weight balance when the HMD is mounted, and the optical system surrounds the face or head of the observer.
FIG. 3 shows an HMD disclosed in Japanese Laid-Open Patent Application No. 5-134208. In this HMD, a single decentered mirror and a relay lens system are arranged so as to surround the observer's face. Referring to FIG. 3, the HMD comprises a decentered mirror 102-1 arranged in front of a pupil 101 of the right eye of the observer, a relay lens system 102-2, and an image generation means 103 such as an LCD. In this HMD, a light beam including image information from the image generation means 103 is transmitted through the relay lens system 102-2 and reflected by the decentered mirror 102-1 to be projected onto the right eye 101 of the observer, thereby displaying an image on the image generation means 103 for the observer as a virtual image. If the decentered mirror 102-1 comprises a half mirror, the observer can observe the image on the image generation means 103 overlapping the scene of the outer field. Note that this HMD also has a portion corresponding to the left eye so that the two, right and left portions are symmetrically arranged on the right and left symmetrical surfaces of the observer's face, but such left portion is not shown in FIG. 3.
When the HMD is constituted using a coaxial lens system, the scene of the outer field cannot be displayed to overlap the image from the image generation means.
When the decentered optical system is used, a so-called see-through type display apparatus which forms an image displayed on the image generation means as a virtual image and displays it to overlap the outer field of view, can be constituted.
On the other hand, in the HMD constituted by using an odd number of decentered mirrors, the image display means is located on the face or head side of the observer. Hence, in order to locate the image display means to avoid the face and/or head of the observer, the entire HMD apparatus tends to become large.